To ensure satisfactory function of the turbine units in a PFBC plant, it is required that the temperature of the air when it passes through compressors is maintained within certain given limits. If this is not done, compressors may, for example, reach a working range where surge occurs.
PFBC plants have been described in a number of patent specifications, technical papers etc. In this description, therefore, only the parts of such a plant which are needed to describe the air system will be briefly described. The Swedish patent application SE 9102651-8 entitled "Air flow control system in PFBC plants", filed concurrently herewith, describes in detail, in addition to the PFBC plant as such, how an air system is built up. It also describes the important limitations that such a system entails and how these are overcome with the aid of controls overriding each other.